What does "aspirate" refer to in the context of vaccine administration?

In the context of vaccine administration, "aspirate" refers to drawing back on the plunger of the syringe to check for blood. This technique is performed after inserting the needle into the muscle to ensure that the needle has not hit a blood vessel. If blood is present in the syringe after aspirating, it indicates that the needle may be in a blood vessel, which could lead to complications if the vaccine is injected into the bloodstream instead of the intended muscle tissue. By aspirating, the healthcare provider ensures that the injection is administered safely and effectively in the correct anatomical location. This practice is critical for certain intramuscular injections to prevent potential adverse reactions.